A diver must know various parameters when he makes an underwater dive in order to ensure his safety. In particular, the diver must instantaneously know the depth at which he is located to avoid the risk of exceeding a pre-established maximum dive depth. The diver must also know his dive time to avoid exhausting his oxygen reserves and in order to ascend to the surface safely. Two other important parameters concern decompression. These parameters are the rate of ascent and the length of any decompression stops. It is of vital importance to know the ascent rate. Indeed, if the diver ascends too quickly, he is at risk of a fatal embolism. The recommended maximum ascent rate is generally 10 m/minute.
CH Patent 513456 discloses a watch provided with mechanisms for indicating the instantaneous depth, immersion time and the minimum length of a decompression stop that the diver might need to observe five metres below the surface. It is noted however that the watch disclosed in this prior art document does not comprise an ascent rate indicator mechanism.
U.S. Pat. No. 3,910,117 discloses a device intended to enable a diver to check his ascent rate. However, this device is not fitted with an ascent rate indicator mechanism. The device disclosed in this prior art document comprises two concentric hands, one intended to indicate the instantaneous depth and the other to simulate the change in depth during a model ascent. Before ascending, the diver makes an adjustment to superpose the two hands. Then, at the moment of starting the ascent, he starts the simulation. During the ascent, the diver constantly checks that the two hands are still superposed, so that his ascent rate is based on that of the model to be followed. One drawback of this prior art device is that it is not possible to change the ascent rate.